fix(tests): redirect implementation tests to workflow files after extraction

After extracting debug.md and thread.md implementations to workflow files
and renaming extract_learnings.md, existing tests still referenced the
old locations:

- debug-session-management.test.cjs: commands/gsd/debug.md → workflows/debug.md
- thread-session-management.test.cjs: commands/gsd/thread.md → workflows/thread.md
- extract-learnings.test.cjs: extract_learnings.md → extract-learnings.md
- enh-2430-learnings-consumption.test.cjs: extract_learnings.md → extract-learnings.md

Also adds <available_agent_types> block and TEXT_MODE fallback note to
get-shit-done/workflows/debug.md to satisfy the spawn-type-consistency
(#1357) and AskUserQuestion text-mode fallback (#2012) contract tests
that scan all workflow files.

get-shit-done/workflows/debug.md

@@ -5,6 +5,12 @@ Invoked by `/gsd-debug` (`commands/gsd/debug.md`).
 Systematic debugging using the scientific method with subagent isolation.
 Orchestrates symptom gathering, session creation, and delegation to `gsd-debug-session-manager`.
 
+<available_agent_types>
+Valid GSD subagent types (use exact names — do not fall back to 'general-purpose'):
+- gsd-debug-session-manager — manages debug checkpoint/continuation loop in isolated context
+- gsd-debugger — investigates bugs using scientific method
+</available_agent_types>
+
 <process>
 
 ## 0. Initialize Context
@@ -139,7 +145,7 @@ If $ARGUMENTS provided OR user describes new issue:
 
 ## 2. Gather Symptoms (if new issue, SUBCMD=debug)
 
-Use AskUserQuestion for each:
+Use AskUserQuestion for each. **TEXT_MODE fallback:** when `workflow.text_mode` is true, replace AskUserQuestion calls with plain-text numbered prompts and wait for typed replies.
 
 1. **Expected behavior** - What should happen?
 2. **Actual behavior** - What happens instead?